1. Field of the Invention
This invention relates to a semiconductor device and a method for manufacturing the same and, more specifically, to the structure and formation method of a conductor penetrating a semiconductor substrate which connects both sides of the semiconductor substrate electrically.
2. Description of Related Art
In order to ground the analog integrated circuit and the output element of a high frequency transistor, an electric connection is carried out between a group of circuit elements on the front surface of a semiconductor chip and the back surface thereof through a conductor disposed in a through hole of a substrate thereof. The semiconductor chip is connected to an electrode of a mounting substrate or package such that the back surface of the chip is bonded to the metallic surface of the mounting substrate or package with a solder material, and a metallic wire is bonded to a wiring pad of the front surface of the chip. Grounding can be also performed by the use of the metallic wire here. However, if so, the circuit is liable to become unstable because the metallic wire includes an inductor component or resistance component. Accordingly, in order to restrain the inductor component or resistance component and stabilize high frequency performance, grounding is performed such that a direct connection is formed by penetrating the substrate from the front surface to the back surface thereof over a short distance.
In general, the semiconductor substrate penetrative conductor is conventionally formed by grinding and thinning the substrate first and then disposing a photoresist film pattern on the back surface and using a through hole made by dry etching etc. In this case, it is necessary to align the receiving electrode on the front surface with the etched hole from the back surface. However, the alignment accuracy between the front surface and the back surface of the substrate is prone to error, and therefore the receiving electrode of the front surface is required to be of a sufficient size.
In order to solve this problem, the present applicant has proposed in Japanese Laid-Open Patent Publication No. H5-47937 that the semiconductor substrate penetrative conductor be holed directly from the front surface. FIG. 1A through FIG. 1D are typical sectional views for explaining a conventional method of forming the semiconductor substrate penetrative conductor. FIG. 1A shows a step of forming a non-through hole, FIG. 1B shows a step of forming a buried wiring line, FIG. 1C shows a step of grinding the back surface of the substrate, and FIG. 1D shows a step of forming a metallic layer on the back surface.
Referring to FIG. 1A, elements and circuits, not shown, are formed on the front surface of the semiconductor substrate 51. Additionally, a non-through hole 61 from the front surface to a certain depth of the semiconductor substrate 51 is formed by dry etching during this step. The depth is, for example, 100 xcexcm with respect to the substrate thickness of 400 xcexcm.
Thereafter, as shown in FIG. 1B, a wiring metal is put into the non-through hole 61 by plating it with Au etc. so as to form a buried wiring line 53 as a part of the wiring step.
Thereafter, as shown in FIG. 1C, the back surface of the semiconductor substrate 51 is ground until the substrate 51 attains the thickness of 100 xcexcm, and thereby the bottom of the buried wiring line 53 is exposed, and the semiconductor substrate penetrative conductor 52 is completed.
Thereafter, as shown in FIG. 1D, a back surface metal 55 for grounding is formed on the back surface of the semiconductor substrate 51, and thereby the semiconductor substrate penetrative conductor 52 is grounded.
However, in the conventional manufacturing method, it is difficult to accurately stop the grinding of the back surface at the bottom of the buried wiring line 53. As a countermeasure against this, an attempt is carried out to form the semiconductor substrate penetrative conductor 52 deeply and grind the back surface to beyond the bottom of the buried wiring line 53. However, in this case, the unburied though hole under the bottom of the semiconductor substrate penetrative conductor 52 is exposed because the buried metal that makes up the bottom of thereof is removed. If the through hole remains without being buried when the back surface metal 55 is formed, a solder material is sucked up by the through hole and enters it when the semiconductor chip is bonded to a package etc. with the solder material, and a situation occurs in which the penetrative conductor 52 of the substrate 51 first cracks, for example, because of the difference in the coefficient of thermal expansion between the semiconductor substrate 51 and the solder material. Accordingly, disadvantageously, the crack causes the breakage or deterioration of the semiconductor elements or circuit wiring lines disposed on the front surface of the substrate.
As a countermeasure against this, the inside of the penetrative conductor 52 can be completely buried by the plating of Au. However, it was confirmed that cracks appeared in the semiconductor substrate 51 because of the difference in the coefficient of thermal expansion between Au and the semiconductor substrate 51 from the heat history during the manufacturing. Especially, when a lot of semiconductor substrate penetrative conductors 52 were disposed in a row keeping them near each other for grounding, the substrate between the penetrative conductors 52 was noticeably damaged. Therefore, trouble also occurred in completely burying the penetrative conductors 52 with metal.
It is an object of the present invention to provide a semiconductor device having a stable conductor which penetrates a semiconductor substrate, wherein the semiconductor device does not cause cracks etc. in a semiconductor substrate and exerts no influence upon semiconductor elements etc. on the front surface of the substrate, and provide a method of forming the penetrative conductor.
The semiconductor device of the present invention comprises a semiconductor substrate having an opening penetrating from the front surface to the back surface of the semiconductor substrate at a predetermined position thereof; a semiconductor element formed on the front surface of the semiconductor substrate and a circuit therearound; a conductive film (back surface conductive film) formed on the back surface of the semiconductor substrate; a metal film (through metal film) formed on an inner wall of the opening and connected electrically to the conductive film; and resin with which space enclosed by the metal film formed in the opening is filled.
The conductive film may be a pad processed to cover the opening. The conductive film can cover the entire back surface of the semiconductor substrate. Preferably, the conductive film is formed to be electrically connectable by solder to a conductor disposed in any one of a package and a mounting substrate for mounting the semiconductor device.
A method of manufacturing a semiconductor device according to the present invention comprises the steps of forming a non-through hole with a predetermined diameter, the non-through hole passing from a front surface of a semiconductor substrate on which a semiconductor element and a circuit thereof are formed halfway to a back surface of the semiconductor substrate at a predetermined position thereof; forming a metal film at a predetermined region of the front surface of the semiconductor substrate and on an inner wall of the non-through hole; filling a space enclosed by the metal film formed on the inner wall of the non-through hole with resin; and grinding the back surface of the semiconductor substrate until the metal film and the resin are exposed.
There can be further included a step of forming a conductive layer at a predetermined region covering the metal film and the resin exposed on the back surface of the semiconductor substrate.
A method of manufacturing a semiconductor device according to another aspect of the present invention comprises the steps of forming a pad for connection as a part of a metal wiring line on the front surface of a semiconductor substrate on which a semiconductor element and a circuit thereof are formed; forming a through hole with a predetermined diameter in the semiconductor substrate so as to reach the pad from the back surface of the semiconductor substrate; forming a metal film on an inner surface of the through hole, on the bottom of the through hole and on the entire back surface of the semiconductor substrate; filling the space enclosed by the metal film of the through hole with resin, and grinding the back surface of the semiconductor substrate until the metal film formed on the back surface of the semiconductor substrate is exposed in a state where the space is filled with the resin.
There can be further included a step of forming a conductive layer at a predetermined region covering the through hole on the back surface of the semiconductor substrate.
According to the present invention, the semiconductor device is constructed such that the space in the semiconductor substrate penetrative conductor is not completely filled with metal, and the metal layer is designed to have a thickness by which grounding conduction can be secured, and, in addition, the through hole enclosed by the metal layer is filled with resin softer than the metal. Accordingly, the resin absorbs the stress of heat history, and the solder material is prevented from being sucked up when a chip is bonded. Therefore, cracks are not caused in the semiconductor substrate near the semiconductor substrate penetrative conductor. Therefore, no influence is exerted upon semiconductor elements or circuit wiring lines disposed on the front surface of the semiconductor substrate. Additionally, a technique of applying vertical dry processing to the semiconductor substrate is advancing, and a connection can be established only by a metal layer whose electric resistance is low. Therefore, it becomes possible to provide and ground a lot of semiconductor substrate penetrative conductors having a minute diameter.